PROJECT 3: PROJECT SUMMARY The overall goal of this proposal is to determine whether the bromodoman and extra-terminal (BET) protein BRD4 is a promising therapeutic target for delaying and/or overcoming resistance to platinum-based ovarian cancer standard of care. Chemoresistance is a major cause of the high mortality of ovarian cancer and in particular in the most common high-grade serous carcinoma (HGSC). Substantial evidence suggests that cells with cancer stem-like cells (CSC) characteristics contribute to chemotherapy resistance. Putative ovarian cancer CSCs are typically characterized by increased aldehyde dehydrogenase (ALDH) activity. This is a hypothesis-driven translational study, and the findings will be pivotal for evaluating whether BET inhibitors in combination with platinum represents an effective approach for overcoming platinum resistance by suppressing ALDH activity in ovarian cancer CSCs. We will collaborate with Incyte, Inc. to use their BET inhibitor INCB57643 that is proven safe in patients. Thus, the BET inhibitor is readily available for immediate translation in ovarian cancer. The proposed studies are based on our recent findings established that inhibition of BRD4 activity by BET inhibitors is sufficient to eradicate ALDH positive CSCs. Our central hypothesis is that platinum resistance can be overcome through eliminating ALDH positive cancer stem-like cells by targeting BRD4 using clinical applicable small molecule BET inhibitor INCB57643. Three Specific Aims are proposed: Aim 1 will explore the combination of BET inhibitor INCB57643 and carboplatin in patients with HGSOC in a Phase 1 clinical trial; Aim 2 will investigate the combinational therapeutic strategy of targeting BRD4 using BET inhibitor INCB57643 and carboplatin in HGSC cell lines and patient-derived xenografts; and Aim 3 will identify companion biomarkers that correlate with response to BET inhibitor INCB57643 and carboplatin combination in HGSOCs. The proposed studies are highly innovative because they challenge current research/clinical paradigms, contribute to new concepts for epigenetic therapeutics by combining BET inhibitors and platinum, and utilize innovative methods to explore new intervention strategies for chemotherapy resistance in ovarian cancer. The proposed studies are of high impact because these studies will develop therapeutic strategies with a durable therapeutic outcome by overcoming platinum resistance through eradicating cancer stem-like cells, a major challenge in the clinical management of ovarian cancer.